Polarization phase shifting for thickness measurement of NiO material transport layer using Sagnac interferometer

The optical interferometric technique with polarization phase shifting has been realized as one of the most important techniques for optical non-contact measurements. However, the measurement of thin film thickness using field emission scanning electron microscopy (FE-SEM) or scanning electron microscopy (SEM) has been inconvenient due to the high cost of maintenance. This research aims to measure the thickness of the Hole Transport Material Nickel (II) oxide (NiO) layer deposited on a glass substrate (NiO/FTO layer) using phase shifting in a Sagnac interferometer. In the experimental setup, the signal is split into the FTO reference arm and the NiO/FTO sample arm using a nonpolarizing beam splitter. The split signals are then detected through a balanced photodetector. By analyzing the signal intensities at polarization settings ranging from 0° to 90°, the phase shift and thickness of the NiO layer can be determined. In this study, a NiO thickness value of 281.64 nm was successfully achieved. To evaluate the accuracy of the proposed measurement method, the percentage error between the proposed technique and the conventional SEM method was computed. The percentage error was found to be 0.23%. These results indicate that the proposed setup holds promise as a cost-effective alternative to SEM for measuring thin film thickness.